The objective is elucidation of the function and structure of the ionic channels in excitable membranes. Experiments are performed usually on squid giant axons that are internally perfused and subjected to voltage clamp. A current objective is an understanding of the relation between opening of the sodium channels and the non-linear component of capacitive current that is called gating current. This is being studied by kinetic analysis, and by the use of substances that interfere with the opening and closing of the channels.